Tennis court surface tester

ABSTRACT

A TESTER FOR TENNIS COURT SURFACES, SUCH AS TEXTILE SURFACES, IN WHICH A TENNIS BALL IS FIRED BY COMPRESSED AIR THROUGH A TUBE INTO A CHAMBER THAT IS PAINTED FLAT BLACK ON THE INSIDE. THE TENNIS BALL STRIKES THE SURFACE TO BE TESTED IN FRONT OF A CAMERA. TWO FALSHING STROBE LIGHTS ARE PROVIDED SO THAT THE CAMERA TAKES A SERIES OF MULTIPLE EXPOSURES OF THE TENNIS BALL. THE ANGLE OF THE EXPOSURE OF THE TENNIS BALLS ON THE WAY DOWN AND ON THE REBOUND CAN BE MEASURED IN PHOTOGRAPHS AND IS A MEASURE OF THE SURFACE TO BE TESTED.

Dec. 7, 1971 JONES I 3,625,052

TENNIS COURT SURFACE TESTER Filed April 1, 1970 2 Sheets-Sheet 1 BALLRECOVERY CHAMBER /3 1 All? CYLINDER 3 ,9

OPEN BOTTOM (TENN/S COURT) fIL-i. I

I N Vlz'N'I'UR.

R0865 E JONES ATTORNEY Dec. 7, 1971 v JONES 3,625,052

TENNIS COURT SURFACE TESTER Filed April 1, 1970 2 Sheets-Sheet 2 If'\'IL'N'I'()R. ROBER F JONES ATTORNEY United States Patent O 3,625,052TENNIS COURT SURFACE TESTER Robert F. Jones, Little Falls, N.J.,assignor to J. P. Stevens & Co., Inc., New York, N.Y. Filed Apr. 1,1970, Ser. No. 24,774 Int. Cl. G01n 3/52, 3/08 US. Cl. 73--79 2 ClaimsABSTRACT OF THE DISCLOSURE A tester for tennis court surfaces, such astextile surfaces, in which a tennis ball is fired by compressed airthrough a tube into a chamber that is painted flat black on the inside.The tennis ball strikes the surface to be tested in front of a camera.Two flashing strobe lights are provided so that the camera takes aseries of multiple exposures of the tennis ball. The angle of theexposures of the tennis ball on the way down and on the rebound can bemeasured in photographs and is a measure of the surface to be tested.

BACKGROUND OF THE INVENTION Tennis court surfaces present a considerableproblem. If a surface is very smooth, for example an asphalt court or asmooth concrete court, there is a tendency for a hard hit ball, such as,for example, a hard serve, to skid some, in other words to rebound at asmaller angle than that at which it strikes the court. This makes itdifficult to return such a ball and is generally considered undesirable.Clay courts and even some grass courts have a sufiicient coeflicient offriction so that skidding of the ball is minimized. However, such courtspresent problems in slow drying after a rain storm, maintenance, and thelike. However, for expert play the smoother asphalt or very smoothconcrete courts are not satisfactory because the surface has too low acoefficient of friction. In recent years various fabrics, such astufted, woven, needle punched, and the like, or extruded or moldedmaterials have been used as covering for courts which would otherwiseshow inadequate coefficients of friction. The carpeting thus producedis, of course, cemented onto the court surface, such as asphalt. Atypical covering or carpeting is described in the co-pending applicationof Depoe and Lombardi, Ser. No. 24,681 filed Apr. 1, 1970, and assignedto the assignee of the present invention. This improved surfacing alsoprovides for rapid drain after a rain storm.

Particularly with textile or other surfaces which are to be cemented onthe court it is important that the coeflicient of friction be as nearideal as possible. Until the present, the only way of determining if asurface had the proper playing characteristics was to rely on playerevaluation, which is a subjective variable. An accurate, simple testerwhich can test the surface or a corresponding sample is thereforeneeded, and it is with an improved form of tester that the presentinvention deals.

SUMMARY OF THE INVENTION The present invention provides exactinformation which can be used in comparing different surfaces beingtested. The invention records the flight of a tennis ball in multipleexposure on film when the ball is fired at a definite angle and adefinite speed and rebounds from a sample of the surface to be tested.The firing of the ball is through an inclined tube by means ofcompressed air or other charge which can be maintained accurately togive a constant velocity. The tubeprojects into a housing painted a fiatblack on the inside, with a recording camera, such as a Polaroid camera,passing through a wall of the chamber at the point where the ballstrikes the surface to be tested. Flashing strobe lights, usually two,result in a series of multiple exposures of the tennis ball, and fromphotographs the exact angle of rebound, which is the most importantfactor, can be measured. Also, another feature of the surface, namelyrebound speed, can be measured on the photograph because the diameter ofthe tennis ball is known and the exact frequency of the flashing lightpermits reliable calculation of speed. For example, if, as is often thecase with a good surface, the ball is moving more rapidly in itstrajectory before it strikes the surface than it does on rebound, themultiple exposures will show the ball images further part on the waytoward the surface than on the rebound. It is thus possible to measureall of the necessary characteristics of a surface from a comparativelysmall sample with precision and accurate reproducibility. As the tennisball is white, it photographs in each flash, whereas the background,which is flat black, remains dark.

If the ball rebounded back off another wall of the housing of the testerit might show in the photograph unless there was a precisely timedshutter opening and closing, which can be provided and which isdesirable in certain preferred embodiments of the invention. Therefore,it is desirable to keep a rebounded ball from coming back into the areawhere photographing takes place and this can be effected by providing aslot through which the ball rebounds into a ball recovery chamber whichretains the ball .and does not permit it to bounce back into the areawhere multiple photography is taking place. This is a preferredmodification, although the device won-ks perfectly well without a ballrecovery chamber if there is a sufliciently precise timing of the camerashutter. Theoretically, of course, a slot through which the reboundingball could pass would be able to permit its return, but the slot isaccurately positioned with respect to the rebound and when the ball goesinto a chamber through the slot and bounces back, chances of itsstriking the slot at exactly the right angle are practically negligible.

One or more flashing strobe lights are mounted inside of the blackenclosure or they may be outside, on its top, and flashing throughopenings in the enclosure into which the strobe lights fit substantiallylight-tight. Both modifications have advantages. The mounting of thestrobe lights inside the enclosure brings them quite close to thetrajectory of the tennis ball on its initial course and rebound and,therefore, sharp multiple photographs can be obtained with minimumintensity of the flashing strobe lights. On the other hand, if thestrobe lights are mounted on top of the enclosure, while they have to besomewhat more intense because they are further away from the twotrajectories of the tennis ball, the mounting permits servicing andsimplifies connecting the strobe lights to their source of electricpulses. The lights are, of course, positioned to illuminate the portionof the surface being tested. It is an advantage of the invention thatthe particular choice of strobe light mounting can be chosen for thebest compromise.

The strobe lights themselves are of standard design, and so in thefurther description and in the drawings their electrical connections arenot shown as they are not changed by the present invention, except ofcourse that the dimensions of the tester determine lengths of supplycables.

As the frequency of flashing should be maintained constant so that speedof rebound as well as angle can be measured, it is desirable to provideaccurate timing, which can be done with conventional solid stateelectronics which deliver accurately timed trigger pulses to relays,such as silicon controlled rectifiers, which permit pulses of highvoltage and high current to the flashing lights. The lights themselvesare, of course, of conventional design, utilizing gaseous dischargetubes.

Since it is desirable to fire the tennis ball each time with either theidentical speed or with speeds which can be adjusted and maintainedconstant, it is preferred to use as the motive force a compressed airsource of comparatively large capacity with a suitable trigger valve.Pressure can be varied with a pressure controlling valve in well knownmanner. These elements, therefore, will be described and shown in thedrawings in diagrammatic form.

The compressed air or other gas container may be outside the testerproper, with a suitable flexible conduit connecting to the balldischarge tube, or it may be mounted on one wall of the containeritself. Other sources of motive power for the tennis ball may also beused, such as explosive cartridges, compressed springs, and the like.However, the use of compressed air is so simple and reliable that itconstitutes the preferred embodiment and will be the one which isdescribed in detail below, although it should be understood that theinvention is not limited to the particular means which impart a definitepredetermined velocity to the tennis ball.

The nature of the camera photographing the flight of the ball is notcritical and any type of camera may be used. However, a Polaroid camera,which permits inspecting a photograph very shortly after it has beentaken, presents so many advantages that it is greatly preferred.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a semi-diagrammatic sectionthrough a surface tester;

FI'G. 2 is a vertical elevation, partly broken away, at right angles toFIG. 1;

FIG. 3 is a multiple exposure photograph of a tennis ball striking andrebounding from a smooth surface, and

FIG. 4 is a similar illustration where the surface has a desirably highcoefficient of friction.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an enclosure, openat its bottom, desig nated :1. The inside of the enclosure is paintedmatte black, and the enclosure is shown set down on the fiat tenniscourt surface. The portion of the tennis court being tested isdesignated 3, which is opposite a camera 2 with lens 15, which can beseen in FIG. 2.

A pair of gaseous discharge strobe lights 4 are mounted underneath thetop of the enclosure. As these lights are conventional, they are shownin diagrammatic form. Supply of powderful high voltage electric pulsesto the flashing lights come in through conventional cables, which areshown symbolically as a pair of wires 16. The rest of the strobe lampsupply is not shown because it is not changed by the present invention.However, the supply should permit flashing at predetermined frequencies,for example 20,000 to 25,000 flashes per minute.

From the left a ball firing tube 5 is shown entering at an angle througha wall 9. The tube has a ball loading chamber 6 and is connected by atube with a compressed air supply 7, preferably having a definitevolume, provided with a regulating valve 13. When a ball is loaded intothe tube and the loading chamber closed, a trigger 12 introduces thecompressed air and is preferably actuated for a sufficient time tointroduce a definite predetermined volume of air. The ball is projectedat 60 or more feet per second through the tube. The ball is shown at 8just before it strikes the surface 3. After striking it, it rebounds, asindicated by the arrow, passing through another slot 10 into a ballrecovery chamber from which the ball can be removed through an opening11 with a suitable closure to prevent entering light during the testing.

The surface 3 is under the housing :1 and a tennis ball is loaded intothe ball loading chamber 6. The trigger 12 is then actuated and a blastof compressed air projects the ball through the tube '5, striking thesurface 3, and rebounding into the ball recovery chamber as shown. Thetrigger 12 can start the strobe lights 4 flashing and open the camerashutter 15 if desired. It is perfectly possible to operate by openingthe camera shutter and starting the strobe light tubes with a manualswitch. However, this results in some additional light even though thewalls of the enclosure are black and the tennis ball has moved throughits path. The particular modification to be chosen depends on a balancebetween darker background as against the additional equipment foropening the camera shutter and/ or starting the lights.

Various surfaces can be tested, for example a sample of hard boardsurface which has a coefficient of friction similar to that of anasphalt surface of an asphalt tennis court. Various textile surfaces canalso be tested, on or off a court.

FIGS. 3 and 4 show two photographs, FIG. 3 being a rebound from smoothhard board and FIG. 4 from a tennis court surface of needle-punchedfabric. It will be seen that the multiple exposures in FIG. 3 representa fairly flat angle which can be measured on the photograph with asuitable movable protractor, whereas in FIG. 4 the carpet surfaceresults in a greater angle of rebound and also a marked slowing down,which is shown by the fact that the multiple exposures of the tennisball are of the same dimensions in FIG. 3, whereas in the rebound theyare more close together as the speed of the ball has been slowed down.

Typically the rebound angle in FIG. 3 is between 28 and 29 and in FIG. 4between 36 and 37. The speed of rebound is about 48 feet per second inFIG. 3 and about 37 feet per second in FIG. 4. This latter figure showsa surface that has substantially ideal coeflicient of frictioncharacteristics and which compares to the best, well maintained, dry,clay courts.

The tester of the present invention is not only useful in testingvarious new surfaces but can be used for monitoring batches of the samedesign of textile to determine if they are uniform and to reject any badbatches.

I claim:

1. A tester for tennis court surfaces comprising in combination,

(a) an open-bottom enclosure having a top, two ends and two side walls,the inside of the enclosure being a non-reflective black and the bottomsof the side and end walls being even so that the enclosure can rest on aflat surface without permitting the entrance of extraneous light,

(b) a recording camera in a side wall at about the middle thereof butnear the bottom,

(c) an inclined tube of tennis ball dimensions in one end wall andinclined so that a projected tennis ball strikes a surface adjacent thecamera lens,

((1) means for loading a tennis ball into the upper end of the tube andclosing it off,

(e) trigger actuated means for imparting a reproducible high velocity tothe tennis ball in the tube, and at least one flashing strobe light atthe top of the enclosure positioned to illuminate the fiat surface to betested, means for actuating the strobe light at a frequency to producemultiple exposures of the tennis ball during both projection and reboundfrom the surface, whereby on actuation of the trigger the tenm's ball isprojected against the surface and rebounds and the trajectories arephotographed by the camera in multiple exposure during each trajectory,the number of multiple exposures in each trajectory being inverselyproportional to the speed of the tennis ball through the trajectory.

2. A tester according to claim 1 having, at the end opposite the ballintroducing tube, a ball recovery chamber separated from the center partof the enclosure of a slot of dimensions permitting a rebounding tennisball to pass therethrough, whereby the rebounding ball is prevented frommoving back into the zone of the flashing lights.

References Cited UNITED STATES PATENTS 10 JAMES J. GILL, PrimaryExaminer E. J. KOCH, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,625,052 Dated December 7, 1971 Inventor(s) Robert F Jones It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 62, "powderful" should be powerful Claim 2, line 3, "of"second occurrence should be by Signed and sealed this 6th day of March1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents ORM kW -10 (lo- USCOMM-DC 69376-P59 {I U S GOVILPHMENTPRINTING OFFICE I969 O]6fi-JJ4

